Elastomeric compounds which can be easily extruded, spunbond or melt blown into elastic fibers or films having low stress relaxation, low hysteresis or permanent set, and high recoverable energy are described in U.S. Pat. Nos. 4,663,220, 4,789,699, 4,970,259, 5,093,422, 5,705,556 and many others. The elastomeric fibers or films are useful in making a variety of applications such as diaper waistbands and non-woven fabrics.
Polystyrene-poly(ethylene-butylene)-polystyrene elastomeric block copolymers have been compounded with other materials such as, for example, polyolefins and tackifying resins to form extrudable elastomeric compositions which can be more easily extruded into elastic fibers or films having improved processing and/or bonding properties. Processes for making cast extruded films, extrusion blown films, extruded fibers, filaments, non-wovens and such like have high requirements around viscosity of the compound. At the same time, applications of these extrudates in personal hygiene, food wrapping and the like result in stringent requirements on mechanical behavior; a combination of stiffness (high modulus), and excellent elasticity (good stress-relaxation and low hysteresis and permanent set) is needed. One of the greatest challenges in this field is to find a good balance between flow/viscosity and the mechanical properties mentioned above.
It is an object of the present invention to provide compositions that have excellent balance of mechanical properties and results in low anisotropy in films derived from them: i.e. the properties of the final film are (almost) equal when measured in machine direction (MD) or traverse direction (TD).
It is also an object of the present invention to provide modified styrene-butadiene block copolymers to be used in said compositions.